A method is described in PCT Application No. WO 2015/120939 A1. When a certain internal pressure is desired in a cavity of a micromechanical component or a gas mixture having a certain chemical composition is to be enclosed in the cavity, the internal pressure or the chemical composition is frequently adjusted during capping of the micromechanical component or during the bonding process between a substrate wafer and a cap wafer. During capping, for example, a cap is connected to a substrate, whereby the cap and the substrate together enclose the cavity. By adjusting the atmosphere or the pressure and/or the chemical composition of the gas mixture present in the surroundings during capping, it is thus possible to adjust the certain internal pressure and/or the certain chemical composition in the cavity.
With the aid of the method described in WO 2015/120939 A1, an internal pressure may be adjusted in a targeted way in a cavity of a micromechanical component. It is in particular possible with the aid of this method to manufacture a micromechanical component having a first cavity, a first pressure and a first chemical composition being adjustable in the first cavity, which differ from a second pressure and a second chemical composition at the time of capping.
In the method for targeted adjusting of an internal pressure in a cavity of a micromechanical component according to WO 2015/120939 A1, a narrow access channel to the cavity is created in the cap or in the cap wafer, or in the substrate or in the sensor wafer. Subsequently, the cavity is flooded with the desired gas and the desired internal pressure via the access channel. Finally, the area around the access channel is locally heated with the aid of a laser, the substrate material liquefies locally and hermetically seals the access channel during solidification.
Another method for adjusting an internal pressure in a cavity of a micromechanical component is described in German Patent Application No. DE 195 37 814 A1. Such a method is provided for manufacturing rotation rate sensors and acceleration sensors. In this method, a plurality of free-standing thick polycrystalline functional structures are manufactured on a substrate, buried strip conductors and electrodes being situated below the functional layers. The micromechanical structures manufactured in this way are sealed with a cap wafer later in the process sequence. A suitable pressure, depending on the use, is enclosed within the sealed volume.
In the case of rotation rate sensors, for example, a very low pressure is enclosed, which is 1 mbar, for example. This is the case, since in rotation rate sensors a portion of the movable structures is resonantly driven. At low pressure, it is possible to very easily induce a vibration with relatively low voltages due to the low attenuation.
In the case of acceleration sensors, however, it is not desirable for the sensor to vibrate, which would be possible if an external acceleration were applied. Hence, these sensors are operated at a higher internal pressure. The internal pressure of an acceleration sensor is 500 mbar, for example.